The present invention relates to an improved rotary drill bit having a bit body with at least one bearing pin attached thereto for rotatably carrying a roller cutter. More particularly, the present invention relates to an improved lubricating and cooling system for the cutter and an arrangement for axially fixing the cutter relative to the bearing pin.
In rotary drill bits, it is common to utilize conical roller cutters which are rotatably carried on bearing pins of the bit body over a bearing system. Satisfactory lubrication and cooling of the bearing system is particularly important. Accordingly, it has been suggested to seal the bearing space at an annular gap formed between the roller cutter and the bit body and to fill the space with a suitable lubricant. However, during operation of such a sealed lubrication system, there is a risk that impurities may penetrate past the seal and enter into the bearing system. Such impurities may cause severe mechanical damage to the bearings. Sealed bearing systems of this type are generally disclosed, for example, in U.S. Pat. Nos. 3,127,942 issued Apr. 7, 1964 to Neilson; 3,964,554 issued June 22, 1976 to Ricks et al; 4,249,781 issued Feb. 10, 1981 to Olschewski et al; 4,298,079 issued Nov. 3, 1981 to Norlander et al; and 4,367,904 issued Jan. 11, 1983 to Olschewski et al.
An alternate proposal has been to provide a continuously flowing fluid, such as air, possibly with an oil mist, to the bearing system in order to avoid the entrance of impurities into the bearing system. However, such a continuously flowing system may not provide sufficient lubrication under all operating conditions of the bit, particularly in a forward portion of the bearing system. An open bearing lubrication system of this general type is disclosed, for example, in U.S. Pat. No. 4,194,794, issued Mar. 25, 1980 to Kling.
It has also been proposed to combine a closed and an open bearing lubrication system within a single rotary rock drill bit. One such combined system is disclosed in U.S. Pat. No. 4,211,453 issued July 8, 1980 to Johansson. In the Johansson patent, the conical cutting elements are secured to a bit segment by annular locking bearings. The locking bearings are fed by a first lubricating system which forces a fluid, preferably water, through angled passages in the bit body and the bit segment past the locking bearings to be expelled externally of the drill bit. A unitary annular seal is provided ahead of the locking bearings for sealing a forward portion of the bearing system including further annular bearings. The forward portion defines a closed space filled with lubricant. Such an arrangement may suffer from the problem of maintaining the integrity of the internal annular seal and ensuring that sufficient cooling of the entire bearing system is accomplished.
A further combined sealed and unsealed lubrication system for rock drill bit bearings is disclosed in U.S. Pat. No. 4,386,668 issued June 7, 1983 to Parish. In the Parish patent, air is supplied through an angled passage in a bearing pin for lubricating a rear bearing of the bearing system. The passage terminates approximately midway on the rear roller bearings to permit fluid to flow rearwardly toward an annular gap between the cutter and the bit body. The cutter is secured on the bit body by a snap ring arranged behind a simple O-ring seal for separating the bearing system into a rear bearing space and a forward bearing space portion. The forward bearing space is filled with lubricant and sealed. Also, a pressure compensating device for the forward bearing space is essential due to the expected rise in the temperature of the lubricant within the forward bearing space. The seal between the forward and rear bearing in the Parish patent is subjected to a substantial amount of heat and friction during operation of the bit. Such heat and friction may cause unacceptable wear on the seal thereby permitting an undesirable amount of leakage of the fluid from the forward bearing space outwardly through the rear bearing. Further, since the air lubricating passage terminates approximately midway on the rollers of the rear bearing, there is no assurance that the entire length of the rear bearing rollers is properly cooled and flushed.
Efforts have also been undertaken in the prior art to develop particularly effective seals for use in rotary drill bits or cutting heads. Such prior art seals include metallic rings biased by an elastomeric element, such as an O-ring, against the surface to be sealed. In other words, the seal is effected between the metal sealing rings and the metal surface. Sealing arrangements of this general type are disclosed in U.S. Pat. No. 3,858,670 issued Jan. 7, 1975 to Ott et al and the aforementioned U.S. Pat. No. 4,367,904 of Olschewski et al. The use of such a seal in a combined open and closed lubrication system, where space considerations are extremely critical, has not been suggested. A further type of seal is disclosed in the previously cited U.S. Pat. No. 4,298,079 issued to Norlander et al. In the Norlander et al patent, a sealing element includes an elastically yieldable tongue biased to a closed position by air pressure. The tongue operates as a first element for preventing the entrance of impurities prior to the impurities reaching the main portion of the seal.
Still further developments have occurred in the prior art for effective arrangements for axially securing a roller cutter element to a bearing pin. In general, the cutting elements are secured by ball bearings (see U.S. Pat. Nos. 3,127,942, 3,964,554 and 4,221,453) or by a snap ring as in the Parish patent discussed above. It has also been suggested to retain the cutting element on the bearing pin by utilizing a set of roller bearings, for example, the rear roller bearings, as shown, in the aforementioned U.S. Pat. Nos. 4,298,079 and 4,256,193.
While numerous advancements have been made in various aspects of rotary drill bit construction, there is still room for improvement. Accordingly, it is an object of the present invention to provide such an improved rotary drill bit which overcomes the various disadvantages of the prior art systems. In particular, it is an object of the present invention to provide a rotary drill bit which includes a highly efficient and effective lubrication and cooling system. The lubrication and cooling system according to the present invention ensures adequate lubrication, prevents the entrance of impurities into the bearing system and effectively cools the entire bearing system. Moreover, the present invention provides an improved sealing arrangement within the bearing system for aiding in accomplishing these objects. Still further, the arrangement according to the present invention is adaptable to existing drill bits without decreasing the overall diameter of the drill bit thereby retaining the full load carrying capacity of the roller cutting elements.
These objects and others are accomplished by a rotary drill bit according to the present invention having at least one roller cutter which is rotatably carried on a bearing pin over a bearing system. The bearing system includes at least a forward bearing and a rear bearing which is a roller bearing. At least one inflow passage is provided in the bit body through which fluid is supplied to the rear bearing during operation of the bit for flushing and for aiding cooling of the rear bearing. The passage terminates in the bearing system ahead of a forward end of the rear bearing between an intermediate sealing arrangement and an outflow passage, preferably in the form of an annular gap provided between the bit body and the roller cutter. The sealing arrangement separates the bearing system into a forward bearing space and a rear bearing space with the forward bearing space being filled with lubricant.
Since the rear bearing lubrication passage terminates ahead of the forward end of the rear bearing rollers, proper lubrication, flushing and cooling of the entire axial length of the rollers is ensured. In accordance with a further aspect of the present invention, the bearing pin includes a flange for axially fixing a forward end of the rollers of the rear bearing with the fluid passage including at least one radially extending passage arranged within the flange. In this way, more effective cooling of the bearing pin, particularly the flange, is accomplished. In particular, since the inflow passage extends further forward in an axial direction than the prior art, more of the bearing pin is cooled by the flowing fluid. Also, by cooling the bearing pin, the lubricant contained within the forward bearing space is also maintained at a lower temperature to reduce expansion of the lubricant therein. In accordance with a further aspect of the present invention, the sealing arrangement is sealed against a forward radial surface of the flange. This arrangement promotes effective cooling of the sealing arrangement due to the proximity of the outlets of the radial passages within the flange to the sealing arrangement.
In a preferred embodiment, the radially extending passages open into the bearing system on an outer peripheral surface of the flange. Further, in a particularly preferred embodiment, six equally angularly spaced radial passages are provided in the flange to more effectively cool both the bearing pin and hence the lubricant within the forward bearing space. Also, the six radial passages more evenly distribute the lubricating air flow to the rear bearing. Still further, the six radial passages are preferably supplied by a single axial passage in the bearing pin in order to reduce the velocity of the air flow through the rear bearing space. In this way, it is ensured that the oil mist entrained within the air flow adheres to the bearing races. If the velocity of the air is too great, the oil tends to be removed or stripped from the bearing races.
Still further in the preferred embodiment, the sealing arrangement includes an angular metallic sealing ring and an elastomeric element for biasing the sealing ring against the forward radial surface of the flange. The elastomeric element is arranged between the sealing ring and an internal surface of the roller cutter such that the elastomeric element remains stationary with respect to both the ring and the cutter.
In accordance with still a further aspect of the present invention, an axial bearing is provided in the forward bearing. The sealing arrangement partially overlaps the axial bearing, which is preferably comprised of a plurality of cylindrical rollers, in an axial direction. In this way, the overall diameter of the roller cutter is not reduced. Moreover, the flange on the bearing pin preferably has a relatively short axial length and the arrangement of the particular seal in overlapping relationship with the axial bearings further reduces the axial space required for these additional elements.
Due to the requirements of maintaining the overall dimensions of the rollers constant, and due to the provision of the flange and the additional seal between the forward and rear bearing spaces, there is insufficient room to provide a locking roller in the form of a ball bearing or a snap ring for axially retaining the cutter as in many of the prior art rotary cutters. In accordance with the present invention, the rollers of the rear bearing, which are axially fixed at a forward end by a rearward surface of the flange, serve to axially fix the roller cutter on the bearing pin. In the preferred embodiment, the axial fixing is accomplished by cooperation of the rear bearing rollers with a shoulder on a rear portion of the roller cutter which shoulder engages a rear end of the rollers of the rear bearing.